Liquid crystal display (LCD) panels are used in many electronic devices to provide an output display of information. As is known by those with skill in the art, conventional LCD fabrication generally involves conductively coating two pieces of patterned glass and placing a liquid crystal material therebetween. A sealant is introduced to enclose the liquid crystal material between the processed glass pieces. The glass is then further processed by means of a photolithographic process into a conductively coated glass piece with selective etching of the conductive areas. An alignment layer is then applied in an orientation necessary to effect a twisted nematic LCD. Usually, the second conductively coated piece of glass is similarly processed with a different electrode pattern and with an alignment layer oriented transverse to the direction of the alignment layer on the first piece of conductively coated glass. Polarizers are often used which are aligned with and adhere to each of the first and second glass surfaces Such LCDs are described in U.S. Pat. No. 4,228,574, Culley et al. at column 1, line 65 through column 2, line 24.
LCDs for use in computer and other types of electronic output displays typically provide a single gray output when the liquid crystal material is charged to its characteristic capacitance to provide output data. It has recently been desirable to provide color displays to electronic devices so that color output can be obtained which is much more pleasing to the eye, and which allows for more detailed and contrasting data to be displayed from the electronic device. In order to make color displays using LCDs, a number of LCDs may be stacked on top of one another to produce such a display. These displays are called "color flat screen displays" and usually contain three individual LCD panels, one for each color; red, green, and blue. The three LCD panels must be mutually aligned such that pixels in each of the LCDs are aligned at the exact location on all three panels.
To minimize a loss of brightness due to light passing through different media corresponding to different colors for each of the three panels, the individual panels are attached together by an adhesive, optically matched material. As the light from an illuminating source passes through the stacked layers, pixels in each panel act as controllable color filters selectively coloring the light exiting the display. This fabrication technique is one of the most common methods of making color flat screen displays using LCD panels. See U.S. Pat. No. 4,917,465, Conner et al., and U.S. Pat. No. 4,966,441, Conner. Stacked LCD displays have drawbacks, for example, parallax, which is found in any stacked optical system. Furthermore, stacked LCDs also provide poor brightness due to absorption of light by the dye in a dyed cell system, and due to blockage of cross-polarized light by polarizers in stacked systems that rely on polarization rotation to differentiate colors. See Conner et al. at column 1, lines 41-47.
A second common approach to fabricating color flat screen displays utilizes a single LCD panel in conjunction with a mosaic colored filter. The mosaic filter typically has a plurality of red, green, and blue filter elements each aligned with a pixel in the single LCD panel. By controlling the transmissivity of pixels in the LCD panel, the display can pass light through selected areas of the color mosaic filter. However, in a color mosaic LCD display, brightness is limited because less than a third of the active area transmits light for any given color. Furthermore, pixel density must be increased by a factor of three to obtain the same resolution as the stacked panel approach. See the Conner et al. patent at column 1, lines 48-66, and the Conner patent at column 1, lines 33-52.
A third approach to fabricating prior color flat screen displays is to use the "birefringence" of color concept which takes advantage of birefringent layers of a liquid crystal material. The birefringent effect is sometimes called "electrically controlled birefringence" or "tunable birefringence" and generally requires applying voltages of different values to a liquid crystal material which will then exhibit different colors based on the different voltages applied. See the Conner et al. patent at column 1, line 67 through column 2, line 17.
It is necessary in birefringent systems to distinguish pixels driven by an "on" voltage from those driven by an "off" voltage. In order to accomplish this distinction, polarizers are used, one to polarize the entering light to a known polarization, and one to select only one polarization of exiting light for examination. See Conner et al. column 2, line 62 through column 3, line 5. Thus, the prior birefringent color flat screen displays as disclosed in the Conner et al. and Conner patents require the use of multiple layer polarizers and color filter elements to provide the full range of color to distinguish between on and off pixels, and to provide suitable brightness to make the LCD screen a viable display device.
In the stacked LCD color flat screens discussed earlier, an adhesive is used to hold the plurality of panels together in the flat screen display. A secondary purpose of the adhesive is to prevent misalignment of the pixels in each of the displays and especially during the manufacturing process. Because the adhesive itself is used to prevent misalignment, the manufacturing process can become very tedious and time consuming, and is also prone to rejects since the surfaces of the LCD panels must be attached, that is, glued together, without air pockets or bubbles. This further requires the need for "clean room" manufacturing since any dust particle or foreign substance which may attach to the tacky surface of the glue or adhesive represents a flaw, and therefore a reject in the manufacturing process.
During the fabrication of such stacked LCD flat color displays, special care must be made during the alignment of the panels since the large area of the glue does not allow for extraneous movement. Prior processes of manufacturing and fabricating color flat screen displays are also prone to induce stresses in the panels thereby producing faults, and any repair or exchange of the faulty panel is not possible.
Laminating liquid crystal material between support members with optically neutral adhesives to make LCD panels is known. See U.S. Pat. No. 4,838,653, Mohebban, at column 8, lines 11-23. In the Mohebban patent, it is taught that an LCD may be fabricated by sandwiching a liquid crystal material between two layers of MYLAR support material. Conductors are etched on the surfaces of the two MYLAR support members and one of the MYLAR support members is then coated on the conductor side with liquid crystal material mixed with an encapsulating medium. This makes the layer of liquid crystal encapsulating medium tacky so that it can be cured in an oven to produce a laminated construction. In this fashion, a LCD with a plurality of liquid crystal elements connected in series can be fabricated. However, the Mohebban patent does not provide a method of fabricating color flat screen displays, and describes a fabrication method which is particularly suited for producing LCD sensors to detect static electricity. See, e.g., column 9, lines 42-50 of the Mohebban patent.
Thus, prior methods of fabricating color flat screen displays fail to provide efficient and economical methods of fabricating display devices utilizing LCD panels. There exists a long-felt need in the art for methods of stacking LCD panels to form color flat screen displays in an expeditious manner. There is a further long-felt need in the art for color flat screen displays which are simple to manufacture, which do not exhibit flaws incurred in the manufacturing process, and which reduce the overall complexity of fabrication.